Electric-furnace resistor



April 14, 1925. 1,533,254

G. M. LITTLE ELECTRI C FURNACE RES I STOR Filed Jan. 25, 1922 fiyz.

flyNEssEs: Ge l/rwEfqg ATTORNEY lid till

Patented Apr. l l, $25.

illallTED GEORGE LITTLE, GE PITTSBURGH, PENNSYLVANIA, ASSIGETQR ELEGTRIC dz MANUFACQLURING COMPANY, A CORPORATION OF Tl) WESTXNGHUUQE PENN$YLVANIA.

ELECTRIC-FURNACE RESISTQR.

a lication filed January 25, 1922. Serial No. senses.

To all whom it may concern:

Be it known that l, GEORGE M. LITTLE, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Electric Furnace Resistors, of which the following is a specification.

My invention relates to electrical furnaces and particularly to electric-resistance furnaces and it has for its object to provide a relatively simple resistor comprising a plurality of formed pieces of carbonaceous material which shall have a relatively high and substantially constant resistance when operated for long periods of time at relatively high temperatures.

W] hen carbonaceous resistors are employed in an electric-resistance furnace to obtain relatively high temperatures it is necessary either to protect the resistor by a suitable refractory envelope or to provide a reducing atmosphere to prevent its oxidation. 1 have found it more advisable to provide a reducing atmosphere in the chamber and my invention has reference more particularly to a "form of carbonaceous resistor which may be employed in a furnace and which shall have a relatively high initial resistance and a substantially constant resistance in the presence of a reducing atmosphere.

in ractising my invention, 1 provide a plu y oi ilat carbonaceous plates sepaaed y relatively short carbonaceous membars, or skeleton form in lateral cross-section, maintained in proper operative position the furnace chamber by resilient oression means. the single sheet of drawings,

igure 1 is a view, in vertical lateral cross-section, of an electric-resistance fur comprising a device embodying my invention.

:2 is a view, in perspective, of a portion of? a resistor embodying my invention, and

to 65, inclusive, are cross-sectional views of various modifications of members of skeleton form embodying my invention.

electric furnace, designated generally by the numeral 11, comprises a metallic framework or casing 12 having a plurality of suitable supporting members 13 secured thereto. An outer lining 1% comprises a plurality or oriclts or blocks of a suitable heat-insulating material. An inner lining 15 comprises a plurality of bricks or blocks of any suitable refractory high-temperatureresisting material, the bricks or blocks of the two linings being so shaped and disposed as to provide a furnace chamber 16 ot any suitable or desired form and dimensions. An opening 17 is provided adjacent the bottom of the chamber 16 to permit of introducing objects to be heated.

A heating element 18 comprises a plurality of relatively thin fiat carbonaceous plates 19 having their flat faces located in adjacent spaced relation relatively to each other and separated by a plurality of members 21, of skeleton form in lateral cross-section, and

represented more particularly in Fig. 2 of the drawing as tubular relatively thin walls. Any number of members may be located between adjacent plates 19 but l have found it preferable to employ three in order to maintain the members 21 in proper operative positions between the adjacent fiat laces oil the members 19 under all conditions of operation.

A relatively heavy plate 22, of carbon or ofgraphite, is located at each end of the built-up heating element 18 and has a depression 23 in the outer surface thereof to receive the inner end of an elongated carbonaceous electrode 24. An opening 25 is provided in the inner portion of the lining 15-410 permit of the electrode at extending therethrough to engage the member 22.. A. water-cooled metallic terminal member 26 is located on the outer end of the electrode being provided with a chamber 2? suitably shaped to engage and co-operate with the outer tapering end of the electrode. This 'self-wedging metallic terminal is described and claimed more in detail in my copending application, Serial No. 463,221, to which reference may had tor the details thereoit.

Resilient compression means for each ele trode may comprise a scriewthreaded stud 28, the inner end of which engages a meta members having too resilient compression means illustrated in the drawing and hereinbefore described is schematic only and suitable or desired compression means may be employed. In order to prevent leakage ofcurrent from the terminal members 26, an insulated annular member 36 may be located in the outer face of the furnace structure immediately surrounding the member 26 and may consist of asblestos or other suitable refractory mater1a I have found that there is a tendency for the two linings of the furnace to separate slightly after repeated cycles of operation of the furnace, which permits air to enter between the linings and flow past the middle portion of the carbonaceous electrodes 24, resulting in an oxidizing action upon the electrode and a consequent wearing away thereof. In order to prevent this, or at least to reduce this oxidizing action, I may pro vide a vertical chamber or well 37 extending from the upper surface of the furnace structure to a small distance below the bottom of each of the carbonaceous electrodes 24 and place therein a mass 38 of granular carbonaceous material. Any oxidizing action of air leaking in, either between the two linings or past the metallic electrode 26, will expend its oxidizing elfect upon the granular material whereby the carbonaceous electrodes 26 are protected while still free to move longitudinall of their own length as the various parts 0 the furnace expand and contract during the operation of the furnace. The granular carboh'aceous material in the wells 37 may be easily renewed and may be tampcd tightly around the electrodes 24 whenever this becomes necessary and the wells may be covered by suitable cover plates 39 placed on the upper surface of the furnace structure. The wells filled with granular carbonaceous material are more particularly described and claimed in my co ending application, Serial N 0. 472,093, to w ich reference may be had for detailed information.

In order to provide a reducing atmosphere I may introduce a hydrocarbonaceous gas into the furnace chamber adjacent the bottom thereof by means of an inlet pipe 41 connected to a suitable supply (not shown), suitable regulating means, such as a valve (not shown), being provided to permit of the regulation of the amount of gas permitted to enter the furnace chamber 16. When this gas is burned in the furnace chamber 16 it produces a sooty vapor which is carried upwardly into the top portion of the furnace chamber in which the heating element 1.8 is located, and the soot is deposited upon not only the entire outer available surface of the heating element but also upon the available surface of the electrodes and upon the furnace walls.

While it is possible to employ a plurality of flat plates 19 to constitute the resistor, the resistance of such resistor is relatively very low and the current value which it is necessary to employ to obtain the relatively high temperatures desired is very large, causing relatively high copper losses in the current leads and the terminal members. It is desirable to increase the resistance of such compound resistor and hence I prefer to employ a plurality of intermediate members of skeleton form, such as are illustrated in Figs. 3 to 6, inclusive, of the drawing. Fig. 3 illustrates a member 42 of substantially I or H-shape in lateral cross-section. Fig. 4 illustrates a member 43 of substantially X-shape in lateral cross-section. The amount of material provided to carry the current may be relatively small by making the walls of the members 42 and 43 relatively thin so that the amount of material provided to carry the current is relatively very small in proportion to the area of the circumscribing perimeter, thus resulting in a relatively high resistance while, at the same time, I obtain a relatively great stability in the built up heating element. Fig. 5 illustrates a member 21 of substantially tubular shape in lateral cross-section and Fig. 6 a member 44 of substantially hollow-square shape in lateral cross-section.

Nhile it is possible to obtain reasonably satisfactory results when members of the type illustrated in Figs. 3 and 4 are employed, the soot deposited not only on the outer surface of the members 42 and 43 but also immediately adjacent to and covering a joint between the edges of the members 42 and 43 and the plates 19 operatively engaged thereby, will be relatively large and result in increasing the conductive area of cross-section of the members of skeleton form to such an extent as to substantially lower the resistance of the built-up heating element. I, therefore, prefer to employ intermediate members such as illustrated in Figs. 5 and 6 which have a protected or covered inner surface upon which no soot may be deposited, thus resulting in a smaller decrease in the efiective resistance of the built-up heating element 18 in actual op eration in the furnace.

As hereinbefore stated, I prefer to employ only three members of skeleton form between each two adjacent plates 19 and I may locate two of these members adjacent the upper edge of the plates 19 and the third one near the central portion of the plate 19 and may also locate the depression 23 in the end members 22 near the upper edge in order that the compression strains caused by the resilient compression means shall be above the center of gravity of the flat plates 19 and be distributed substantially equally over the members of skeleton form. The lower portion of the plates 19 serves to protect the members 21 against oxidation and against the deposit soot thereon.

.The device embodying my invention thus provides a relatively simple built-up carbonaceous resistor member employing alternate flat carbonaceous plates and intermediate carbonaceous members of skeleton form whereby I obtain a carbonaceous resistor having a relatively high initial resistance and also am able to maintain said initial resistance at more nearly its original value. Y While I have illustrated a specific embodiment of my invention, I do not wish to be limited thereto and. desire that only such limitations shall beplaced thereon as are imposed by the prior art'or are specifically set forth in the appended claims.

I claim as my invention 1, An electric furnace comprising a plurality of relatively thin, fiat, carbonaceous plates, and a plurality of relatively short carbonaceous members, of skeleton form in lateral cross-section, located in spaced relation between the flat faces of said plates, and means for producing a sooty vapor in said furnace, said plates embodying means for reducing 'the deposit of soot on said members of skeleton form.

2. An electric furnace comprising a plurality of relatively thin, flat, carbonaceous plates, and a plurality of relativel short carbonaceous members, of skeleton orm in lateral cross-section, located in spaced relation between the flat faces of said plates,

and means for producing a sooty vapor in said furnace, said plates embodying means for reducing the deposit of soot on said members of skeleton form, and for reducing the oxidation of said members.

In testimony whereof, I have hereunto subscribed my name this 27th day of December, 1921.

GEORGE M. LITTLE. 

